The teleseismic tomography study by P-wave traveltime data beneath the southern South-north Seismic Zone

The southern South-north Seismic Zone is situated in the southeastern margin of the Tibetan plateau, where is a tectonic transitional zone between the Tibetan plateau and the Yangtze craton. We use the teleseismic tomography method to image the three dimension velocity structures beneath the southern South-north Seismic Zone, which has the scientific implication for revealing the uplift mechanism of the Tibetan plateau and the evolution of the plate tectonics. We collected the teleseismic waveform data recorded by the 90 permanent broadband seismic stations and 356 portable broadband seismic stations. The 88691 P-wave traveltime residuals were picked with the waveform correlation method. We obtained the three dimension P-wave velocity structures beneath the southern South-north Seismic Zone by the FMTT (Fast Marching Teleseismic Tomography). With the checkboard tests, we found that the scale of anomalies with 1 degrees X 1 degrees X 100 km could be recovered perfectly in most study area. The tomographic results with good resolution illuminate that the three dimension velocity structures are robust and reliable. The three dimension P-wave velocities reveal that the deep structures of the study area present significant inhomogeneities that the Tengchong volcanic region indicates the obvious low P-wave velocities, but the southwest of the Sichuan basin and the deep Baoshan block suggest the remarkable high P-wave velocities. Through analyzing our results determined by the teleseismic tomography, we draw several conclusions: 1) There is a low velocity anomaly above 400 km beneath the Tengchong volcanic region; 2) A high velocity anomaly down to 300 km beneath the southwestern Sichuan basin; 3) The obviously low velocity anomalies exist along the fault belts around the Chuandian diamond block and the south of the Chuandian diamond block, which provide a necessary channel for the lateral extrusion of the Tibetan plateau materials toward to the southeast; 4) The eastward-dipping high velocity anomaly belt beneath the Baoshan block imply the subducted eastwardly lithosphere of Indian plate.